Variable cam phaser for automobile engine

ABSTRACT

The invention provides a variable cam phaser for an automobile engine, equipped with a self-locking mechanism which is simpler in structure, cost effective, and easy to manufacture. The self-locking mechanism includes: a eccentric circular members ( 12 ) integral with the camshaft ( 6 ) and a support groove ( 15 ) for supporting the eccentric circular members from the both sides thereof at positions offset from the camshaft axis towards the eccentric cam center; a lock plate integrally held with the control rotor by means of a coupling mechanism; and a cylindrical portion belonging to the drive rotor in which the lock plate is inscribed. The self-locking mechanism prevents an unexpected change in the phase angle caused by an external disturbing toque transmitted to the camshaft via the crankshaft of the engine.

TECHNICAL FIELD OF THE INVENTION

This invention relates to a variable cam phaser for an automobile enginefor varying the relative phase angle between the crankshaft of theengine and the camshaft of the apparatus to change open/close timing ofvalves of the engine, the apparatus equipped with a self-lockingmechanism for preventing an unexpected change in the phase angle causedby an external disturbing torque transmitted from the valve.

BACKGROUND ART

Such variable cam phaser as stated above equipped with a self-lockingmechanism for preventing such unexpected change in phase angle isdisclosed in Patent Document 1 listed below. This Patent Document 1teaches a multiplicity of eccentric circular members (eccentric circularcam 110, first link 111, second link 112) each member having aneccentric center and arranged at a prescribed axial position of thecamshaft such that the four centers of the eccentric members function asa whole as a four-link mechanism 108. By putting a brake on thefour-link mechanism 108 with a first or second electromagnetic clutch105 or 106, respectively, via a first or second control rotor 102 or103, respectively, the phase angle of the drive rotor 101, operableconnected to the camshaft and crankshaft, can be changed relative to thecamshaft.

This four-link mechanism 108 can vary the relative phase angle betweenthe camshaft and crankshaft (drive rotor 101) in the phase advancing orretarding direction through rotations of the eccentric circular cam 110integral with the camshaft, first link 111 rotatably supported by theeccentric circular cam 110, and second link 112 rotatably supported bythe first link 111 about their pivots in association with a brakedmovement of either the first or second control rotor 102 or 103,respectively.

On the other hand, when the camshaft is subjected to an externaldisturbing torque arising from a reaction of a valve spring andtransmitted to the drive rotor 101, the first link 111 is pressedagainst a guide groove 113 of the first link formed in the drivecylinder 115 of the drive rotor 101, so that the circular eccentricmembers 110-112 are unrotatably fixed, thereby preventing the camshaftfrom changing its phase angle relative to the drive rotor 101. Thevariable cam phaser disclosed in Patent Document 1 has a self-lockingmechanism for preventing any phase angle change caused by such externaldisturbing torque as discussed above.

PRIOR ART DOCUMENT

PATENT DOCUMENT 1 PCT/JP2009/61327

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Since the self-locking mechanism disclosed in Patent Document 1 has afour-link mechanism 108, the self-locking mechanism must achieveself-locking function with a required accuracy of the four-linkmechanism 108. As a consequence, the self-locking mechanism turns out tobe very complex and costly. Thus, a need exists to provide a simpleself-locking mechanism.

It is, therefore, an object of the present invention to provide astructurally simpler and more cost effective variable cam phaser forautomobile engine having a self-locking mechanism.

Means for Solving the Problem

An inventive variable cam phaser for an automobile engine as recited inclaim 1 includes:

a drive rotor driven by the crankshaft of the engine;

a control rotor;

a camshaft coaxial with the drive rotor and adapted to rotatably supportthe drive rotor;

a torque means for providing the control rotor with a torque forrotating the control rotor relative to the drive rotor;

a phase angle varying mechanism for varying the relative phase anglebetween the drive rotor and the control rotor in accord with therelative rotation of the control rotor relative to the drive rotor; anda self-locking mechanism mounted in the phase varying mechanism forpreventing a phase change from occurring between the drive rotor and thecamshaft caused by an unexpected cam torque appearing on the camshaft,the variable cam phaser characterized in that the self-locking mechanismcomprises:

an eccentric circular cam integral with the camshaft; and

a lock plate having

-   -   a support groove for supporting, at positions further offset        from the camshaft axis in the direction (referred to as        eccentric direction) from the camshaft axis towards the cam        center of the eccentric circular cam, the periphery of the        eccentric circular cam from both sides thereof,    -   a coupling mechanism for transmitting the relative rotational        torque from the control rotor to the eccentric circular cam, and

a cylindrical body formed integral with the drive rotor andcircumscribing the periphery of the lock plate.

(Function) Upon receipt of an external disturbing torque from a valve,the lock plate in rotation together with the camshaft is subjected to asubstantially radial force via the support groove that is adapted toimmovably holding the eccentric circular cam integral with the camshaft,and hence the lock plate is pressed against the cylinder of the driverotor. As a consequence, the drive rotor and the camshaft both driven bythe crankshaft are interlocked and prohibited from undergoing a relativerotation by the external disturbing torque, thereby keeping the phaseangle between them unchanged.

As recited in claim 2, the phase angle varying apparatus of claim 1 maybe configured such that:

the support groove extends in a radial direction of the lock plate;

the eccentric circular cam is provided on the outer periphery thereofwith a lock plate bush; and

the lock plate bush has on the opposite sides of the outer peripherythereof a pair of flat faces spaced apart across the line of eccentricdirection and supported by the support groove.

(Function) With the eccentric circular cam held in the support grooveand with the lock plate bush kept in surface contact with the supportgroove via the paired flat faces, the contact stress generated on thewall of the support groove is reduced as compared with the stress thatwould be otherwise generated if the eccentric circular cam were indirect contact with the support groove. As a result, substantially nouneven friction wear will take place in contacting surfaces, whichallows the lock plate and eccentric circular cam to be kept in goodcondition without suffering a backlash or play, which in turnfacilitates prompt generation and transmission of a pressure between thelock plate and the cylinder of the drive rotor under an externaldisturbing torque.

As recited in claim 3, the variable cam phaser of claim 2 may be furtherconfigured such that the lock plate is divided into two parts by a pairof slits each extending from the support groove to the periphery of thelock plate.

(Function) When the eccentric circular cam is held in surface contactwith the support groove of the lock plate via the lock plate bush, itmay happen that the torque that causes the lock plate to rotate relativeto the cylinder under an external disturbing torque becomes dominantover the radial force that forces the lock plate against the cylinder ofthe drive rotor, thereby rendering the self lock mechanism inoperable.However, when the lock plate is divided into two part by the slitsextending from the support groove to the periphery of the lock plate,the relative torque generated on one of the divided lock plateconstituent members is not well transmitted to the other member. As aconsequence, under an external disturbing torque, the torque generatedon the entire lock plate is reduced. Accordingly, the pressure exertedto the drive rotor cylinder of the lock plate is enhanced.

As recited in claim 4, the variable cam phaser of claim 3 may beconfigured such that one of the two slits may be provided with means forproviding a force to widen that slit (said means hereinafter referred toas urging means).

(Function) By providing one of the slits with such force to widen one ofthe slits, the gaps that are formed during manufacture between the lockplate and drive rotor cylinder and between the lock plate bush and thesupport groove are reduced, thereby reducing the plays of members of theself-locking mechanism during self-locking operation. That is, apressure needed to force the lock plate against the drive rotor cylindercan be instantaneously generated under an external disturbing torque.

As recited in claim 5, the variable cam phaser of claim 2 may beconfigured such that the lock plate is provided with two slits extendingfrom the support groove to the periphery of the lock plate and that theradius of curvatures of the lock plate on the opposite sides thereofacross the line of eccentric direction are slightly larger than theinner radius of the cylinder circumscribing the lock-plate.

(Function) The lock plate inscribed in the cylinder has a slightlylarger radius of curvature than the inner radius of the cylinder, and isacted upon by a radially inward forces exerted by the cylinder. As aconsequence, the gaps between the lock plates and the drive rotorcylinder and between the lock plate bush and the support groove, formedby manufacturing errors for example, are still reduced. That is, in thisconfiguration, as in the configuration defined in claim 4, clearances(plays) of members of self-locking mechanism are reduced during aself-locking operation under an external disturbing torque, and thud arequired pressure to the drive rotor cylinder of the lock plate isinstantly generated.

As recited in claim 6, the variable cam phaser defined in claim 4 or 5may be further configured such that the lock plate bush is divided intotwo parts by a pair of slits.

(Function) In this configuration, as defined in claim 6, since a forceis exerted on each of the divided members of the lock plate bush by theurging means via the lock plate, gaps that are formed between thedivided lock plate bushes and the eccentric circular cam can be reducedin size than the gaps formed with undivided lock plate bushes, so thatthe plays of self-locking constituent members are still reduced. Thatis, a pressure created by an external disturbing torque is instantlytransmitted to the drive rotor cylinder. This implies that precisionrequirement for the eccentric circular cam and rock plate bush can berelaxed and hence the production costs of the self-locking mechanism canbe reduced.

Further, as recited in claim 7, the variable cam phaser defined in anyone of claims 2 through 6 may be configured such that the flat faces ofthe lock plate bushes are a pair of stepped faces projecting to theright and left with respect to the line of eccentric direction, and thatthe stepped faces are offset in the eccentric direction away from thecam center towards the eccentric axis of the cam center.

(Function) Strictly speaking, a gap due to manufacturing error is formedbetween the support groove and the respective lock plate bushes.However, when the flat faces are stepped and abutted against the rockplate at positions offset from the cam center of the eccentric circularcam, the arcuate moving distance traveled by the flat faces before theycome into contact with the support groove under an external disturbingtorque is reduced as compared with the case where the planes are notstepped. In other words, plays of the rock plate bushes are stillminimized then, so that a still instantaneous pressure is generated andtransmitted to the drive rotor cylinder of the lock plates under anexternal disturbing torque.

Still further, as recited in claim 8, the variable cam phaser defined inany one of claims 1 through 7 may be configured such that the couplingmechanism consists of coupling members each engaging with one of pairedcoupling holes formed in the control rotor and with one of pairedcoupling holes formed in the rock plate; and that a minute clearance isprovided between each coupling member and an associated coupling hole ofeither the control rotor or the lock plate.

(Function) If the positional relationship between the control rotor andthe lock plate is set too strict, a manufacturing error may make itdifficult to press the lock plate against the drive rotor cylinder underan external disturbing torque. By providing a minute clearance betweeneach of the coupling members and the associated hole, the lock plate isless restricted to move in the radial direction, which makes it easy forthe lock plate to be pressed against the drive rotor cylinder under anexternal disturbing torque.

Results of the Invention

The variable cam phaser for automobile engine defined in claim 1 has aself-locking mechanism which is simpler in structure and cost effectivethan conventional one in that the mechanism consists of such members asa drive rotor cylinder, disc shaped lock plate, and support groove.

The variable cam phaser in accordance with claim 2 is equipped with aself-locking mechanism having an improved self-locking function anddurability.

The variable cam phaser in accordance with any one of claims 3 through 8has a still improved self-locking function.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective figure of a variable cam phaser for anautomobile engine in accordance with a first embodiment of theinvention, as viewed from the front end thereof.

FIG. 2 is an exploded perspective figure of the apparatus of FIG. 1, asviewed from the rear end thereof.

FIG. 3 is a front view of the apparatus of the first embodiment(excluding cover 70).

FIG. 4 is a cross section taken along line A-A of FIG. 3.

FIG. 5 is a cross section taken along line E-E of FIG. 4.

FIG. 6 shows cross sections of the apparatus taken along line B-B ofFIG. 4 (FIG. 6( a)) and along line C-C of FIG. 4 (FIG. 6( b)).

FIG. 7 illustrates a self-locking mechanism of the first embodiment.

FIG. 8 is a cross section of a self-loci mechanism in accordance with asecond embodiment of the invention, taken long a line that correspondsto line E-E of FIG. 4.

FIG. 9 illustrates a variation of a spring member used in the secondembodiment.

FIG. 10 illustrates a variation of the lock plates.

FIG. 11 is a cross section of a self-locking mechanism in accordancewith a third embodiment of the invention, taken along a line thatcorresponds to line E-E of FIG. 4.

BEST MODE FOR CARRYING OUT THE INVENTION

The invention will now be described in detail by way of example withreference to the accompanying drawings. variable cam phaser shown in therespective embodiments are installed in an automobile engine, adapted totransmit the rotation of the crankshaft of the engine to the camshaft ofthe apparatus to open/close air suction/exhaustion valves of the enginein synchronism with the crankshaft so that the valve timing of the airsuction/exhaustion valves is changed in accord with such parameters ofthe operating conditions of the engine as an engine load and rpm.

Referring to FIGS. 1 through 6, there is shown a structure of a firstembodiment of the invention. A variable cam phaser 1 comprises a driverotor 2 driven by the crankshaft, a first control rotor 3 (referred toas control rotor in claim 1), a camshaft 6 (FIG. 4), torque means 9, aphase angle varying mechanism 10, and a self-locking mechanism 11. Theend of the apparatus having a second electromagnetic clutch shown inFIG. 1 will be hereinafter referred to as the front end, while the endhaving the drive rotor 2 will be referred to as the rear end. Therotational direction (clockwise direction) of the drive rotor 2 aboutthe axis L0 of the camshaft as viewed from the front end will bereferred to as phase advancing direction D1, and the opposite rotationaldirection (counterclockwise direction) will be referred to as phaseretarding direction D2.

The drive rotor 2 consists of a sprocket 4 and a drive cylinder 5 havinga cylinder 20, integrated together with a multiplicity of bolts 2 a. Thecamshaft 6 shown in FIG. 4 is immovably and coaxially integrated withthe rear end of a center shaft 7 by means of a bolt 37 screwed into athreaded female hole 6 a formed in the front end of the camshaft and thecentral circular hole 7 e of the center shaft 7.

The first control rotor 3 is a generally bottomed cylinder having aflange portion 3 a at the front edge thereof, a cylindrical portion 3 bextending rearward, and a bottom 3 c. The bottom 3 c has a centralcircular throughhole 3 d, a pair of pin holes 28, an arcuate groove 30extending along a circle of a given radius about the central axis L0(the groove hereinafter referred to as arcuate groove 30), and a guidegroove 31 whose radius decreases in the phase advancing direction D1about the central axis L0 (the groove hereinafter referred to as obliqueguide groove 31).

The center shaft 7 is a contiguous body comprising a first cylindricalportion 7 a, flange portion 7 b, second cylindrical portion 7 c,eccentric circular cam 12 having a cam center L1 eccentrically offsetfrom the camshaft axis L0, and a third cylindrical portion 7 d, arrangedalong the axis L0 in the order mentioned from the rear end towards thefront end. The drive rotor 2 comprises a sprocket 4 and a drive cylinder5 which are integrated together by means of bolts 2 a. Provided betweenthe sprocket 4 and the drive cylinder 5 is a center shaft 7, which has aflange portion 7 b. The center shaft 7 also has first and secondcylindrical portions 7 a and 7 c, respectively, which are fitted in thecircular hole 4 a of the sprocket 4 and in the circular hole 5 a of thedrive cylinder 5 a, respectively, so that the drive rotor 2 is rotatablymounted on the camshaft 6 via the center shaft 7. The third cylindricalportion 7 d is fitted in the central circular hole 3 d of the firstcontrol rotor 3. It is noted that the drive rotor 2, first control rotor3, camshaft 6, and center shaft 7 are coaxial with the axis L0.

The torque means 9 consists of a first electromagnetic clutch 21 forproviding the first control rotor 3 with a first torque (braking torqueto retard the control rotor 3 relative to the drive rotor 2), and areverse rotation mechanism 22 for providing the first control rotor 3with a second torque which is opposite in direction with respect to thefirst torque.

The phase angle varying mechanism 10 includes the center shaft 7(rotatably supporting the drive rotor 2), self-locking 11, and acoupling mechanism 16, and is adapted to couple the first control rotor3 unrotatably with the camshaft 6.

The self-locking mechanism 11 is arranged between the drive rotor 2 andcenter shaft 7 so as to prevent a phase angle disturbance from occurringbetween the drive rotor 2 and camshaft 6 under an external disturbingtorque applied to the camshaft 6 by a valve spring (not shown). Theself-locking mechanism 11 consists of the eccentric circular cam 12 ofthe center shaft 7, lock plate bush 13 and lock plate 14, and thecylinder 20 of the drive rotor 2.

The lock plate bush 13 has a circular hole 13 a for receiving thereinthe eccentric circular cam 12 of the center shaft 7, and is provided onthe opposite sides thereof with a pair of flat faces 23 and 24, as shownin FIGS. 1 and 5. The lock plate bush 13 is rotatably mounted on theperiphery of the eccentric circular cam 12 such that the two flat faces23 and 24 are maintained substantially parallel with respect to a lineL2 connecting the camshaft axis L0 and the cam center L1 as shown inFIG. 5.

The lock plate 14 is generally disk shaped and has a substantiallyrectangular support groove 15 extending along a diameter. The lock plate14 consists of a pair of two constituent members 14 a and 14 b dividedby a pair of slits 25 and 26 formed at the opposite narrow sides 15 aand 15 b of the support groove 15 and extending to the circumference ofthe lock plate 14. The flat faces 23 and 24 of the lock plate bush 13are held in contact with the long sides 15 c and 15 d of the supportgroove 15.

The periphery of the lock plate 14 is inscribed in the cylindricalportion 20 of the drive cylinder 5. The flat faces 23 and 24 of the lockplate bush 13 are sandwiched between the long sides (15 c and 15 d) ofthe support groove 15. Under this condition, the portion of theperiphery of the eccentric circular cam 12 eccentrically offset (fromthe cam center L1) beyond a line L3 that passes through the cam centerL1 perpendicularly to the line L2 is supported by the support groove 15via the lock plate bush 13.

The coupling mechanism 16 consists of a pair of coupling pins 27, a pairof first pin holes 28 formed in the bottom 3 b of the first controlrotor 3, and a pair of second pin holes 29 each formed in the respectiveconstituent members 14 a and 14 b of the lock plate 14. Each of thecoupling pins 27 is fixedly fitted at one end thereof in either thefirst pin hole 28 or second pin hole 29, but at the other end looselyfitted in the other first pin hole or second pin hole with a minute gapbetween pin and the hole. The lock plate 14 is pressed against the innercircumferential surface 20 a of the cylinder 20 of the drive cylinder 5and unrotatably held therein when an external disturbing torque istransmitted thereto, as described in detail later. The minute gapprovided in either the first or second pin hole 28 or 29 is tocircumvent a difficulty of pressing the lock plate 14 against the innercircumferential surface 20 a if the lock plate 14 is fixed to the firstcontrol rotor 3.

The lock plate 14, inscribed in the cylinder 20 of the drive cylinder 5and holding the lock plate bush 13 therein, is unrotatably integratedwith the first control rotor 3 by means of the coupling pins 27 insertedthe first and second pin 28 and 29. As a consequence, the center shaft 7(camshaft 6) is unrotatably integrated with the first control rotor 3via the eccentric circular cam 12, lock plate bush 13 and lock plate 14.

The camshaft 6 becomes integral with the first control rotor 3 under anexternal disturbing torque exerted by the torque means 9, and undergoesa relative rotation relative to the drive rotor 2 in either thephase-advancing direction D1 or phase retarding direction D2. As aresult, the phase angle between the camshaft 6 and drive rotor 2 (or acrankshaft, not shown) is changed, thereby changing the valve timing.

It is noted here in connection with the torque means 9 that the firstelectromagnetic clutch 21 is firmly secured inside the engine (notshown) ahead of the first control rotor 3. When the front end 3 e of theflange portion 3 a is attracted by the first electromagnetic clutch 21onto the friction member 21 a of the first electromagnetic clutch 21,the first control rotor 3 is retarded in rotation relative to the driverotor 2 rotating in D1 direction.

The reverse rotation mechanism 22 consists of the arcuate groove 30 andthe oblique guide groove 31 of the first control rotor 3, a secondcontrol rotor 32, a disk shaped pin guide plate 33, a secondelectromagnetic clutch 38 for putting a brake on the second controlrotor 32, first and second link pins 34 and 35, and a ring member 36.

The second control rotor 32 is arranged inside the cylindrical portion 3b of the first control rotor 3 and rotatably mounted on the coaxialthird cylindrical portion 7 d of the center shaft 7 that passes throughthe central circular throughhole 32 a of the second control rotor 32.The second control rotor 32 is provided in a rear section thereof with astepped eccentric circular hole 32 b, whose center of is offset from thecamshaft axis L0. The ring member 36 is slidably inscribed in thestepped eccentric circular hole 32 b.

The disc shaped pin guide plate 33 is arranged inside the cylindricalportion 3 b of the first control rotor 3 and between the bottom 3 c andsecond control rotor 32 such that the pin guide plate 33 is rotatablysupported by the third cylindrical portion passing through the centralcircular throughhole 33 a of the pin guide plate 33. The pin guide plate33 has a groove 33 b and a guide groove 33 c that extends independentlyof the circular throughhole 33 a in substantially opposite radialdirections (the guide grooves hereinafter referred to as radial guidegrooves). The radial groove 33 b is formed in correspondence with thearcuate groove 30 and extends from a position near the central circularthroughhole 33 a to the periphery of the pin guide plate. The radialguide groove 33 c is formed in correspondence with the oblique guidegroove 31 and extends to a point near the periphery.

A thin round shaft 34 a and a thick hollow shaft 34 b integrated withthe thin round shaft 34 a at the front end of the thin round shaft 34 aconstitutes a first link pin 34. The thick hollow shaft 34 b issupported on both sides thereof by the radial groove 33 b. The rear endof the thin round shaft 34 a passes through the arcuate groove 30 andsupport groove 15, and is securely fixed to a mounting hole 5 b of thedrive cylinder 5. On the other hand, the thin round shaft 34 a can movein the arcuate groove 30 between the opposite ends of the arcuate groove30.

A second link pin 35 consists of a first member 35 c which is made up ofa thin shaft 35 a integrally connected to the rear end of a thick roundshaft 35 b, a first hollow shaft 35 d, a second hollow shaft 35 e, and athird hollow shaft 35 f. The first through third hollow shafts 35 d-35 fare mounted in sequence on the thin round shaft 35 a and retainedtogether at their rear ends. The thick round shaft 35 b is inserted inthe support groove 15. The first hollow shaft 35 d has an arcuateperiphery that can fit the oblique guide groove 31, and is movable alongthe oblique guide groove 31 with its upper and lower sides supported bythe oblique guide groove 31. The second hollow shaft 35 e has acylindrical shape and is movable along the radial guide groove 33 c withits opposite sides held by the radial guide groove 33 c. The thirdhollow shaft 35 f has a cylindrical shape and is rotatably fitted in thecircular hole 36 a formed in the ring member 36.

It is noted that a holder 39 and a washer 40 each having a centralcircular hole 39 a and 40 a, respectively, are placed on the leading endof the third cylindrical portion 7 d of the center shaft 7 The holder39, washer 40, and center shaft 7 are securely fixed to the camshaft 6with the bolt 37 screwed into a threaded bore 6 a through the circularholes 39 a, 40 a, and 7 e. As a result, all the elements between thedrive rotor 2 and the second control rotor 2 inclusive, arranged roundthe periphery of the center shaft 7, are securely fixed together betweenthe flange portion 6 b of the camshaft 6 and the holder 39. The axialclearance of these elements can be optimized by adjusting the thicknessof the washer 40. Arranged in front of the bolt and the first and secondelectromagnetic clutches 21 and 38, respectively, is a cover 70.

The operation of the torque means 9 for changing the phase angle betweenthe camshaft 6 and drive rotor 2 (and the crankshaft not shown) will nowbe described. Normally, the first control rotor 3 is in rotation in D1direction (FIG. 6) together with the drive rotor 2 When the firstcontrol rotor 3 is attracted by, and abutted against, the firstelectromagnetic clutch 21 for braking, the center shaft 7 (camshaft 6)is retarded in D2 direction together with the integrated first controlrotor 3, relative to the drive rotor 2 which is rotating in D1direction. As a consequence, the phase angle of the camshaft 6 relativeto the drive rotor 2 (and of the crankshaft not shown) is varied in thephase retarding direction D2, thereby changing the open/close timing ofthe valve.

Under this condition, the first hollow shaft 35 d of the second link pin35 moves in the oblique guide groove 31 in substantially the clockwisedirection D3 (FIG. 6( c)), and the second hollow shaft 35 e moves in theradial guide groove 33 c in D4 direction towards the axis L0 (FIG. 6(b)). Thus, the third hollow shaft 35 f shown in FIG. 6( a) provides thering member 36 with a torque that causes the ring member 36 to slidewithin the circular hole 32 b. The thin round shaft 34 a moves in thearcuate groove 30 in the clockwise direction D1. The opposite ends 30 aand 30 b of the arcuate groove 30 serve as stoppers for stopping thethin hollow shaft 34 a that comes into abutment with the ends.

On the other hand, the second control rotor 32 is normally in rotationin D1 direction together with the drive rotor 2 (FIG. 6( a)) As thesecond electromagnetic clutch 38 is activated, the front end 32 c of thesecond control rotor 32 is attracted onto the friction member 38 a,resulting in a rotational delay of the second control rotor 32 in D2direction relative to the first control rotor 3. In response to theeccentric rotation of the stepped eccentric circular hole 32 b in D2direction within the ring member 36 shown in FIG. 6( a), the ring member36 slidably rotates in the stepped eccentric circular hole 32 b. Inresponse to the movement of the ring member 36, the second hollow shaft35 e shown in FIG. 6( b) moves in the radial direction D5 within theradial guide groove 33 c together with the third hollow shaft 35 f andfirst hollow shaft 35 d. In this case, the first control rotor 3 shownin FIG. 6( c) is acted upon by a torque in the direction opposite to thetorque generated by the first electromagnetic clutch 21. This torque isexerted, via the wall of the oblique groove 31, by the first hollowshaft 35 d moving in the oblique groove 31 in the substantiallycounterclockwise direction D6, causing the first control rotor 3 to berotated in the phase advancing direction D1 still more relative to thedrive rotor 2 rotating in D1 direction. Accordingly, the phase angle ofthe camshaft 6 relative to the drive rotor 2 (and crankshaft not shown)is advanced in D1 direction back to the original phase angle, therebyrestoring the open/close timing of the valve.

Next, operation of the self-locking mechanism 11 will now be describedin detail. The phase angle of the center shaft 7 (and of the camshaft 6)relative to the drive rotor 2 (and of the crankshaft not shown) isdetermined by a rotation of the first control rotor 3 in the phaseadvancing direction D1 or retarding direction D2 relative to the driverotor 2, as described above. However, if an external disturbing torqueis transmitted from a valve spring (not shown) to the camshaft 6, therelative phase angle between the camshaft and drive rotor 2 is changed,which will result in an unexpected deviation in open/close timing of thevalve. The self-locking mechanism 11 of this embodiment takes advantageof such external disturbing torque to prevent such phase angledeviation.

FIG. 7 illustrates how a self-lock function takes place between theperiphery (14 c and 14 d) of the lock plate 14 and the cylinder 20 ofthe drive cylinder 5 when an external disturbing torque is transmittedto rotate the camshaft 6 (center shaft 7) in clockwise direction D1 orcounterclockwise direction D2.

When the camshaft 6 and the center shaft 7 are subjected to an externaldisturbing torque in the phase retarding direction D2 or phase advancingdirection D1, the eccentric circular cam 12 is acted upon by a torquethat causes the cam center L1 to be eccentrically rotated about thecamshaft axis L0 in either D2 direction or D1 direction. Assume nowthat: the cam axis L1 is eccentrically offset from the camshaft axis L0by a distance s; line L2 passes through the axis L0 and cam center L1;and line L3 passing through the cam center L1 is perpendicular to lineL2; and line L3 intersects the eccentric circular cam 12 at point P1.Under this condition, when the eccentric circular cam 12 is subjected toa torque in the in D2 direction, the guide plate bush 13 is acted uponby a force F1 exerted by the eccentric circular cam 12 at theintersection point P1 in the direction of line L3. When the eccentriccircular cam 12 is acted upon by an external disturbing torque in D1direction, the lock plate bush 13 is acted upon by a force F2 exerted bythe eccentric circular cam 12 at intersection point P2 along line L3(directed from cam center L1 to intersection point P2).

It is noted that the forces F1 and F2 are transmitted along line L3 fromthe lock plate bush 13 to the lock plate 14 via the flat faces 23 and 24in surface contact with the respective long sides 15 c and 15 d of thesupport groove 15. These forces F1 and F2 are further transmitted fromperipheries of the constituent members 14 a and 14 b, respectively, ofthe lock plate 14 to the inner circumferential surface 20 a of the drivecylinder 5 at points P3 and P4 where line L3 meets the peripheries ofthe constituent members 14 a and 14 b.

Local frictional forces arise at points P3 and P4 from the forces F1 andF2 between the inner circumferential surface 20 a of drive cylinder 5and the peripheries 14 c and 14 d that prevent a relative rotation ofdrive cylinder 5 relative to the lock plate 14. These local frictionalforces can be determined as follows. Denoting by L4 the tangential linesof the respective peripheries of the constituent members (14 c and 14 d)at the intersection points P3 and P4; by L5 a line perpendicular to lineL3; by L6 a line perpendicular to line L4; by θ1 and θ2 the angles(hereinafter referred to as friction angles) of lines L5 and L6 at theintersection points P3 and P4, respectively. with respect to thetangential line L4; and by μ the friction coefficient of the frictionalsurface, the forces acting on the drive rotor 2 at the intersectionpoints P3 and P4, respectively, that may cause a phase angle deviationbetween the drive rotor 2 and camshaft 6 are given by F1*sin θ1 andF2*sin θ2, respectively. The local frictional forces preventing slidesthat may occur between the inner circumferential surface 20 a and theperipheries 14 c and 14 d are given by μμF1*cos θ1 and μ*F2*cos θ2,respectively.

When the frictional forces exceed the forces that can incur a phaseangle chance, the drive cylinder 5 and the lock plate 14 are firmlysecured to each other. Then, the lock plate bush 13 and the eccentriccircular cam 12 (center shaft 7) are also immovably secured to eachother. As a consequence, the control rotor 2 and camshaft 6 areimmovably locked to each other under the external disturbing torque,thereby resulting in no relative phase change between them.

In the case when the following conditions

F1*sin θ1<μ*F1*cos θ1

and F2*sin θ2<μ*F2*cos θ2

are satisfied, the local frictional forces preventing the sliding motionof the lock plate 14 with respect to the drive cylinder 5 exceeds theforce that can cause an angular phase change, so that a self-lockingfunction is established between them. Thus, by setting the frictionangles θ1 and θ2 such that

θ1<tan⁻¹ μ and θ2<tan⁻¹ μ,

the self-locking takes place between the drive rotor 2 (or thecrankshaft not shown) and the camshaft 6 under an external disturbingtorque, thereby preventing a change in phase-angle.

It is noted that if the lock plate bush 13 having flat faces 23 and 24is inserted between the eccentric circular cam 12 and support groove 15,the contact stresses that appear on the support groove 15 in surfacecontact with the long sides 15 c and 15 d will be reduced. However, theself-locking function can be established even if the eccentric circularcam 12 is held in the support groove 15 with the line L2 passing throughthe axis L0 and L1 aligned with the long sides 15 c and 15 dsubstantially in parallel thereto. Thus, the lock plate bush 13 may beomitted.

Next, referring to FIG. 8, there is shown a self-locking mechanism 41 inaccordance with a second embodiment of the invention. The self-lockingmechanism 41 has substantially the same elements as the firstself-locking mechanism 11 except that lock plate bush 42 and lock plate43 have different shapes from the corresponding lock plate bush and lockplate of the first embodiment. A spring member 44 corresponds to theurging means of claim 4.

Specifically, the lock plate bush 42 is similar in shape to the lockplate bush 13 of the first embodiment, except that the lock plate bush42 has no flat faces like 23 or 24. In the second embodiment, the lockplate 43 is provided with a slit 46 and a slit 47 for mounting a springmember 44. Thus, the slit 47 is larger than the slit 46. Other featuresof the lock plate 43 are the same as those of the lock plate 14.

The lock plate bush 42 is mounted on the eccentric circular cam 12 thatpasses through the circular hole 42 a of the lock plate 42. The lockplate bush 42 has a substantially elongate rectangular support groove 45extending in a substantially diametrical direction. The lock plate bush42 is divided into two constituent members 43 a and 43 b by a pair oflinear slits that extend radially outwardly from the short sides 45 aand 45 b of the support groove 45 to the periphery of the lock plate 43.The slit 46 has the same shape as the slit 25 of the lock plate 14 ofthe first embodiment, but the slit 47 differs from the slit 26 of thefirst embodiment in that the slit 47 has a larger width than slit 46.

Mounted in the slit 47 is a spring member 44, which has an arcuateconvex portion 44 a and curved portions 44 b and 44 c at the oppositeends of the arcuate convex portion 44 a, where the width of the arcuateconvex portion 44 a is larger than the that of the slit 47. A springmember 44 provides the constituent members 43 a and 43 b with a forcefor widening the width of the slit 47 when its arcuate convex portion 44a is fitted in the slit 47 and the curved portions 44 b and 44 c aresupported by the constituent members 43 a and 43 b. As a consequence, inthe self-locking mechanism 41, any gaps introduced during manufacturebetween the peripheries 43 c and 43 d of the constituent members 43 aand 43 b and the inner circumferential surface 20 a of the drivecylinder 5, and between the lock plate bush 42 and support groove 45 arereduced, thereby reducing plays of these members, and hence improvingthe pressure transmission to the inner circumferential surface 20 a ofthe lock plate 43 in self-locking action. Thus, a positive self-lockingfunction is established.

An external disturbing torque is transmitted from the cam center L1 ofthe eccentric circular cam 12 to the inner circumferential surface 20 aof drive cylinder 5 along line L3, and generates forces F1 and F2 at theintersection points P7 and P8, which forces are transmitted from thelock plate bush 42 to the respective constituent members 43 a and 43 bthrough line contact between the lock plate bush 42 and the lock plateconstituent members 43 a and 43 b at the intersection point P5 and P6 ofthe tangential line L3 with the periphery of the lock plate bush 42.Further, these forces acts on the inner circumferential surface 20 a ofthe drive cylinder 5 at the intersection points P7 and P8 of line L3with the peripheral surface (43 c and 43 d). In this case, as in thefirst embodiment, by setting the friction angles between the tangentiallines passing through the intersection point P7 and P8 and the lineperpendicular to line L3 (the friction angles corresponding to thefriction angles θ1 and θ2 defined in the first embodiment) in the rangea self-locking function is established between the lock plate 43 and thecylinder 20 of the drive cylinder 5 under an external disturbing torque.

It is noted that the urging means for widening the width of the slit 47is not limited to the 44 as shown in FIG. 8: it may alternatively be atrapezoidal member 48 a and a spring member 48 b as shown in FIG. 9( a)and (b). As shown in FIG. 9( a), the lock plate 43 has cut-away portions47 a and 47 b that narrows in diameter along the camshaft axis L0 andtowards the periphery of the slit 47. A trapezoidal member 48 a isarranged between the cut-away portions 47 a and 47 b. The trapezoidalmember 48 a is provided in the periphery thereof with a recess 48 c forreceiving a spring member 48 b corresponding to the spring member 44.The trapezoidal member 48 a is acted upon by a spring force exerted bythe spring member 48 b in the direction D7 towards the axis L0. Thisforce will act on the faces of the cut-away portions 47 a and 47 b atright angle thereto, thereby widening the slit 47.

As shown in FIG. 9( b), a C-shaped leaf spring 49 for compressing thelock plate constituent members 43 a and 43 b is arranged round theperipheries of the lock plate constituent members so as to widen thewidth of the slit 47 and narrow the width of the slit 46. The C-shapedleaf spring 49 is arranged such that its opening is aligned with theslit 46 between the lock plate constituent members 43 a and 43 b.Further, the left half portion of the C-shaped leaf spring 49 shown inFIG. 9( b) may be fixed to the constituent member the 43 b with theright half of the C-shaped leaf spring 49 while the right half portionmounted on the constituent member 43 b so that the constituent member 43b is urged to rotate in the D2 direction relative to the constituentmember 43 a. Thus, the peripheries of the lock plate constituent members43 a and 43 b are urged to move towards the inner circumferentialsurface 20 a of the drive cylinder 5 by the C-shaped leaf spring 49. Asa consequence, gaps formed between the inner circumferential surface 20a of the drive cylinder 5 and the peripheries 43 c and 43 d of the lockplate 43, and between a lock plate bush 50 and the support groove 45 aswell due to manufacturing errors, are reduced by the urging force of theC-shaped leaf spring 49, and so are the plays of the associatedelements.

As shown in FIG. 9( b), the lock plate bush 50 may be split into twolock plate bush constituent members 50 a and 50 b separated by slits 50c and 50 d formed along line L2. When the lock plate bush 50 is divided,the gaps formed between the inner periphery 50 e of the lock plate bush50 and the outer periphery of the eccentric circular cam 12 due tomanufacturing errors are still reduced, thereby further reducing playsof the constituent members and providing still effective self-lockingfunction. Since plays of the locking members due to manufacturing errorscan be reduced with the urging means as shown in FIGS. 8 and 9,precision requirements for the eccentric circular cam 12, lock platebush 42 and 50, and for rock plate 43 can be relaxed to lower theproduction cost.

This lock plate may be made in the form of a C-shaped object 51 havingan opening or slit 53 that extends from a support groove 52 to the outerperiphery 51 a of the C-shaped object 51 as shown in FIG. 10, whereinthe outer diameter of the C-shaped object 51 (as measured along line L3)can be made slightly larger than the inner diameter of the innerperiphery 20 a of the cylinder 20 so that the inner periphery 20 a areconstantly pushed radially outward (in the direction of d2 and d3 inFIG. 10). In this configuration, the same self-locking function asdescribed above in connection with FIGS. 8 and 9 can be obtained withoutthe spring member.

Next, referring to FIG. 11, there is shown another self-lockingmechanism for use with an automobile variable cam phaser in accordancewith a third embodiment of the invention. The self-locking mechanism 61has essentially the same structure as the second self-locking mechanism41 except that the spring member 44 is removed from the washer 40 andthat the lock plate bush 42 is replaced by a lock plate bush 62 having adifferent configuration.

The lock plate bush 62 has a pair of right and left stepped faces 63 and64, respectively, each having a flat face 62 a/62 b and stepped portion62 c/62 d projecting therefrom to the right/left.

The lock plate bush 62 is mounted on the eccentric circular cam 12coaxially with the eccentric circular cam 12 that passes through thecircular hole 62 e of the lock plate bush 62 such that the stepped faces63 and 64 are parallel to line L2 extending from the axis L0 toward theL1. On the other hand, the stepped faces 63 and 64 are mounted on theeccentric circular cam 12 in a symmetric fashion with respect to line L2and offset from the cam center L1. In other words, provided in a regionof the lock plate 62 further offset from the intersection points C1 andC2 where line L3 intersects the flat faces 62 a and 62 b, are thestepped faces 63 and 64 projecting to the right and left of the flatfaces 62 a and 62 b. Line L7 connecting the centers of the flat faces 63and 64 is substantially parallel to line L3, and intersects line L2 at aright angle at point C3 which is eccentrically further offset from thecamshaft axis L0 than the cam center L1. The stepped faces 63 and 64 areheld in position by the long sides 45 a and 45 b of the support groove45.

As the eccentric circular cam 12 is acted upon by a force in D2direction or D1 direction due to an external disturbing torque, the longsides 45 a and 45 b of the support groove 45 are respectively subjectedto outward forces oriented to the left and right direction,respectively, along line L7, across the stepped faces 63 and 64 whichare in surface contact with long sides 45 a and 45 b of the supportgroove 45 at positions further offset than the cam center L1 of theeccentric camshaft 12. Furthermore, the forces F3 and F4 are transmittedfrom the lock plate 43 to the inner circumferential surface 20 a of thedrive cylinder 5 at the intersection points P9 and P10 where line L7intersects the outer peripheries 43 c and 43 d of the lock plateconstituent members 43 a and 43 b, respectively. Thus, these forces aretransmitted from the cylinder 20 of the drive cylinder 5 to the lockplate 43. In this case, by setting the friction angles θ1 and θ2 betweenthe tangential lines at intersection points P9 and P10 and the lineperpendicular to line L7 to satisfy

θ1<tan⁻¹ μ,θ2<tan⁻¹ μ

in the same manner as the friction angles defined in the firstembodiment, a self-locking function is established between the lockplate 43 and the cylinder 20 of the drive cylinder 5 by an externaldisturbing torque.

It is noted that minute gaps exist between the stepped faces 63 and 64and the support face 45 due to manufacturing errors. In the thirdembodiment, however, the stepped faces 63 and 64 are in contact with thesupport face 45 at further offset positions than the cam axis L1 of theeccentric circular cam 12 that they exhibit less plays in theself-locking mechanism as compared with the first embodiment in whichthe eccentric circular cam 12 only has non-stepped flat faces 23 and 24.This is due to the fact that, if such minute gaps exist, an externaldisturbing toque facilitates the flat faces to move round the axis L0until the flat faces come into contact with the support groove 45,whereby the stepped faces 63 and 64 (offset from the cam center L1) arein contact with the support groove 15 at positions further offset fromthe cam center L1 than the non-stepped faces 23 and 24 of the eccentriccircular cam 12 of the first embodiment, so that the distance from thepoint of surface contact to the rotational axis is longer in the thirdembodiment than in the first embodiment. As a consequence, fluctuationsin phase angle caused by the gaps are more reduced in the thirdembodiment for a given gap than in the first embodiment. As a result, byreducing the plays involved in the self-locking mechanism, the pressurethat acts on the cylinder 20 of the lock plate 43 under an externaldisturbing torque is enhanced, thereby securing the function of theself-locking mechanism. This is true if the spring member 44 is removedfrom the slit 47.

BRIEF DESCRIPTION OF SYMBOLS

-   1 variable cam phaser for automobile engine-   2 drive rotor-   3 first control rotor (control rotor of claim 1)-   6 camshaft-   9 torque means-   10 phase angle varying mechanism-   11 self-locking mechanism-   121 eccentric circular cam-   13 lock plate bush-   14 lock plate-   14 a and 14 b lock plate constituent members-   15 support groove-   16 coupling mechanism-   20 cylindrical portion-   23 & 24 a pair of flat faces-   25 & 26 a pair of slits-   27 coupling members-   28 coupling holes of control rotor-   29 coupling holes of lock plate-   44 means (spring member)-   50 lock plate bush-   51 C-shape lock plate-   53 slit-   63 & 64 stepped face-   L0 camshaft axis-   L1 cam center of eccentric circular cam

1. A variable cam phaser for an automobile engine including: a driverotor driven by the crankshaft of the engine; a control rotor; acamshaft coaxial with the drive rotor and adapted to rotatably supportthe drive rotor; a torque means for providing the control rotor with atorque for rotating the control rotor relative to the drive rotor; aphase angle varying mechanism for varying the relative phase anglebetween the drive rotor and the control rotor in accord with therelative rotation of the control rotor relative to the drive rotor; anda self-locking mechanism mounted in the phase varying mechanism forpreventing a phase change from occurring between the drive rotor and thecamshaft caused by an unexpected cam torque appearing on the camshaft,the variable cam phaser characterized in that the self-locking mechanismcomprises: an eccentric circular cam integral with the camshaft; and alock plate having a support groove for supporting, at positions furtheroffset from the camshaft axis in the direction (referred to as eccentricdirection) from the camshaft axis towards the cam center of theeccentric circular cam, the periphery of the eccentric circular cam fromboth sides thereof, a coupling mechanism for transmitting the relativerotational torque from the control rotor to the eccentric circular cam,and a cylindrical body formed integral with the drive rotor andcircumscribing the periphery of the lock plate.
 2. The variable camphaser according to claim 1, wherein the support groove extends in aradial direction of the lock plate; the eccentric circular cam isprovided on the outer periphery thereof with a lock plate bush; and thelock plate bush has on the opposite sides of the outer periphery thereofa pair of flat faces spaced apart across the line of eccentric directionand supported by the support groove.
 3. The variable cam phaseraccording to claim 2, wherein the lock plate is divided into two partsby a pair of slits each extending from the support groove to theperiphery of the lock plate.
 4. The variable cam phaser according toclaim 3, wherein one of the two slits may be provided with urging meansfor providing a force to widen that slit.
 5. The variable cam phaseraccording to claim 2, wherein the lock plate is provided with two slitsextending from the support groove to the periphery of the lock plate;and the radius of curvatures of the lock plate on the opposite sidesthereof across the line of eccentric direction are slightly larger thanthe inner radius of the cylinder circumscribing the lock-plate.
 6. Thevariable cam phaser according to claim 4, wherein the lock plate bush isdivided into two parts by a pair of slits.
 7. The variable cam phaseraccording to claim 3, wherein the flat faces of the lock plate bush area pair of stepped faces projecting to the right and left to the line ofeccentric direction; and the stepped faces are offset in the eccentricdirection away from the cam center towards the eccentric axis of the camcenter.
 8. The variable cam phaser according to claim 3, wherein thecoupling mechanism consists of coupling members each engaging with oneof paired coupling holes formed in the control rotor and with one ofpaired coupling holes formed in the rock plate; and a minute clearanceis provided between each coupling member and an associated coupling holeof either the control rotor or the lock plate.
 9. The variable camphaser according to claim 5, wherein the lock plate bush is divided intotwo parts by a pair of slits.
 10. The variable cam phaser according toclaim 4, wherein the flat faces of the lock plate bush are a pair ofstepped faces projecting to the right and left to the line of eccentricdirection; and the stepped faces are offset in the eccentric directionaway from the cam center towards the eccentric axis of the cam center.11. The variable cam phaser according to claim 5, wherein the flat facesof the lock plate bush are a pair of stepped faces projecting to theright and left to the line of eccentric direction; and the stepped facesare offset in the eccentric direction away from the cam center towardsthe eccentric axis of the cam center.
 12. The variable cam phaseraccording to claim 6, wherein the flat faces of the lock plate bush area pair of stepped faces projecting to the right and left to the line ofeccentric direction; and the stepped faces are offset in the eccentricdirection away from the cam center towards the eccentric axis of the camcenter.
 13. The variable cam phaser according to claim 4, wherein thecoupling mechanism consists of coupling members each engaging with oneof paired coupling holes formed in the control rotor and with one ofpaired coupling holes formed in the rock plate; and a minute clearanceis provided between each coupling member and an associated coupling holeof either the control rotor or the lock plate.
 14. The variable camphaser according to claim 5, wherein the coupling mechanism consists ofcoupling members each engaging with one of paired coupling holes formedin the control rotor and with one of paired coupling holes formed in therock plate; and a minute clearance is provided between each couplingmember and an associated coupling hole of either the control rotor orthe lock plate.
 15. The variable cam phaser according to claim 6,wherein the coupling mechanism consists of coupling members eachengaging with one of paired coupling holes formed in the control rotorand with one of paired coupling holes formed in the rock plate; and aminute clearance is provided between each coupling member and anassociated coupling hole of either the control rotor or the lock plate.16. The variable cam phaser according to claim 7, wherein the couplingmechanism consists of coupling members each engaging with one of pairedcoupling holes formed in the control rotor and with one of pairedcoupling holes formed in the rock plate; and a minute clearance isprovided between each coupling member and an associated coupling hole ofeither the control rotor or the lock plate.